Just fired up my 406sbc Saturday for the break in, the break in went well but afterward when I rev it up the fan belt keeps turning around upside down on the pulleys, and threw it once, I have tightened the belt loosened it got a longer belt, short belt, nothing seem to work, every time I rev it up to about 3500rpm the belt rolls around upside down on the pulleys, one time before it rolled over smoke was coming off the belt down at the crank pulley when I revved it.
The pulleys look like they might be out of alignment but I put a level across them and it looked like the water pump pulley sticks out a very small fraction of inch, maybe 1/16, I don�t think that�s the problem.

Almost forgot, these are the same brackets, pulleys, water pump, and alt from the old motor that had no problem with belts.

Do I need to go to serpentine pulleys and belts?

Do the serpentine belts grip better?

Any suggestions are welcome.

406chevelle

I would try a narrower belt. It will ride down in the pulleys deeper and should take care of the problem. As an example if your belt number now is a 50017 get a 50015 or 50013. The last digits are the width. Make sure the alt brackets are not flexing. I also run the shortest belt i can. I usually weld the slot up in the top bracket so it only has about 1" of movement. This will help strengthen it up.....

The serpentine belts work good by do use a little more horsepower to run.

Keith

Thanks Keith, I did not know about the width think.

I guess you run a shorter belt so there are no long sections of belt to move/flop around?

On the other hand a longer belt has more surface contact with the pulleys.

I am going to get narrower short belt and give it a shot, if that doesn’t work I’ll try a longer one.

What about running dual belts?

Mean time I will be watching for more suggestions on pulleys.

Thanks again Keith.

406chevelle

There is a phenomenon that happens with belts that cause the alternator to suddenly speed up. it's kinda the same thing as cracking a whip. I know there is a name for it but i don't recall it off the top of my head.....

This is why i try to run the shortest belt i can because the longer the belt the worse the wip. All in all i am not sure how much of a difference it is.

I have had the belt rolling and flying off problem before and the narrow belt,, short sturdy bracket has fixed it 100 percent of the time ,,, For me anyway...


Keith

[color=lightblue][size=3]Doc here:

Another thing, and I didn't know this until the Napa Parts guy told me after the 3 RD set of belts in one day, on my rebuilt engine, Newly Painted Pulleys Will roll and throw Belts...

Don't Know if he was right, But I scuffed them up a bit with a brass acid brush, and a year later, I'm still running on set 3.....

As I said, I'd never heard of it before, but it did seem to cure the problem.

Also did All the Spacers go back in the proper locations, Had an Altenator That Looked right, but it had an ever~so~slight angle in it...played havoc with the belts.

Doc
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The story is true Doc. The paint peels off into one big clump and throws the belt. Its good to scuff the paint on any new pulley esp. for better grip on the belt.
Alignment is the next problem to check for.
The brackets may mount and fit, BUT the alignment can be off centerline and throw a belt.

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[color=lightblue][size=3]Doc again:

Those two Items fixed The problem for me...

The Alternator was so far enough out so as not to detect the fact that it was slightly crooked by eye, Until I shot a Carpenter's Laser Level Inferred Line across it.

Prior to the Engine rebuild, It would run for months at a time before blowing a belt. It would also burn up the Bearings on the Alternator, and The waterpump. Turned out to be the Spacer was slightly undersize and tightening up the adjuster arm just slightly bent it. So when I put the New Pulleys on and encountered the problem, I fixed both at the same time...and haven't had a problem since!

BTW Nice Ride 1Bad80, Is that a RAY hood on yours?

Doc


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Many times a belt rolling over in the pulleys is caused by the belt being an end belt. An end belt is a defective belt that comes from the end of the slab or tube that the belts are cut from. Most times the belt will have discernable taper when you flip the belt inside-out. The taper itself does not cause the roll-over but the belt not having cord all the way across the belt construction. 406Chevelle-This does not sound like your problem, though, as you stated that you have tried different belts. I've been cutting belts for 20 yrs at a Goodyear plant and after that long a person kind-of knows a bad belt from a good belt. All of Goodyear Gatorback V-belts are now made in MEXICO and are very poor quality compared to what they used to be when they were made in the US. When I started working there, they had 1800 people working in production, now about 450. All jobs went to Mexico and Canada. I'll be glad to answer anyone's belt questions if I can. Myron-

All V belts are now made metric. All the old GM fan pulleys were designed for a fraction size belt. A modern metric V belt does not sit in the old fraction size pulleys right and will slip and flip over at high rpm.

Go to the junk yard and get the fan, alt and crank pulleys off a third gen camaro or firebird (85-87) with a carb (305) and the wider flat rib belt system.
The flat rib fan belt is a lot more stable at high rpm.

Any job that is lost in the US is not going to Canada, trust me.

If you can find the third gen with the serpentine setup still on it? I looked for a month and a half the found one 700 mile away